Stanislav Opluštil

A comparative analysis of some Late Carboniferous basins of Variscan Europe

Vegetation diversity and pattern changes, and their relation to tectono-sedimentary histories are compared between selected Euramerican Late Palaeozoic coalfields, to understand better the controls on the dynamics of the Pennsylvanian terrestrial ecosystems and to demonstrate the problems with comparing data from various basins. The analysis is based on data from the following basins of different geotectonic and palaeogeographical positions: the cratonic Pennines Basin, the foreland South Wales and Upper Silesia basins, and the fault-related Intra Sudetic and Central and Western Bohemia basins. The analysis indicates that complex factors are responsible for changes in plant diversity and vegetation patterns. These are related to climate, tectonics, preservation potential, sampling biases and the current state of revision of the flora in each basin. Plant diversity patterns in the basins differ because of local controls and/or the character and detail of the available data. Maximum diversity varies among the basins within the Langsettian and Duckmantian substages. Two apparent step-like drops in diversity were detected within coal-bearing strata of most basins: at the Duckmantian/Bolsovian boundary and at the Bolsovian/Asturian boundary. Further and more prominent falls are related to transitions from coal-bearing to non-coal-bearing (mostly red bed) strata or vice versa during Stephanian times. Interpretation of climatic signals recorded in the sedimentary successions indicates that Westphalian and middle Stephanian times were wet intervals, whereas early and late Stephanian times were drier.

Late Moscovian terrestrial biotas and palaeoenvironments of Variscan Euramerica

A synthesis of the upper Moscovian sedimentological and palaeontological record of terrestrial habitats across the Variscan foreland and adjacent intramontane basins (an area which is referred to here as Variscan Euramerica) suggests a contraction and progressive westward shift of the coal swamps. These changes can be correlated with pulses of tectonic activity (tectonic phases) resulting from the northwards migration of the Variscan Front. This tectonic activity caused disruption to the landscapes and drainage patterns where the coal swamps were growing, which became less suitable to growth of the dominant plants of the swamps, the arborescent lycopsids. They were progressively replaced by vegetation dominated by marattialean ferns, which through a combination of slower growth and larger canopies resulted in less evapo-transpiration. This in turn caused localised reductions in rainfall, which further affected the ability of the lycopsids to dominate the swamp vegetation. These changes were initially localised and where the coal swamps were able to survive the lycopsids and pteridosperms show little change in either species diversity or biogeography, indicating that at this time there was minimal regional-scale climate change taking place. By Asturian times, however, the process had accelerated and the swamps in Variscan Euramerica became progressively replaced by predominantly conifer and cordaite vegetation that favoured much drier substrates. Except in localised pockets in intramontane basins of the Variscan Mountains, the last development of coal swamps in Variscan Euramerica was of early Cantabrian age. Further west, lycopsid-dominated coal swamps persisted for a little longer. The last remnants of the lycopsid-dominated coal swamps in the Illinois Basin disappeared probably by middle-late Cantabrian times, as the cycle of contracting wetlands and regional reductions in rainfall generated its own momentum, and no longer needed the impetus of tectonic instability. This tectonically-driven decline in the Euramerican coal swamps was probably responsible for an annual increase in atmospheric CO 2 of c. 0.37 ppm, and may have been implicated in the marked increase in global temperatures near the Moscovian – Kasimovian boundary, and the onset of the Late Pennsylvanian interglacial.

Two species of Selaginella cones and their spores from the Bohemian Carboniferous continental basins of the Czech Republic.

Two species of Selaginella cones from the Bohemian Upper Carboniferous continental basins of the Bolsovian and Westphalian D age are described, together with their in situ spores. Two specimens of Selaginella gutbierii yielded microspores closely comparable with the dispersed species Cirratriradites saturnii and megaspores closely comparable with the dispersed species Triangulatisporites vermiculatus. Microspores closely comparable with the dispersed species Cirratriradites annulatus and megaspores resemble the dispersed species Triangulatisporites tertius were isolated from cones of Selaginella cf. leptostachys. All the spores isolated from one cone are of the same type and would be referred to one dispersed micro- and megaspore species if found as Sporae dispersae. The paper contains a review of all palynologically studied Carboniferous Selaginella and Selaginella-like cones and reviews of all in situ and dispersed Cirratriradites and Triangulatisporites spores.

Composition and structure of an in situ Middle Pennsylvanian peat-forming plant assemblage buried in volcanic ash, Radnice Basin (Czech Republic)

Abstract A three-dimensional reconstruction is provided of the composition, spatial distribution, and structure of a single-aged, Middle Pennsylvanian (Moscovian) peat-forming forest of a high-ash, planar (rheotrophic) mire, buried in situ by volcanic ash and preserved in the Lower Radnice Coal of the Radnice Basin (Czech Republic). The reconstruction is based on a detailed taxonomic and taphonomic analysis of fossils in a ∼0.5-m-thick tuff bed at the base of the Whetstone Horizon excavated over an area of 93.5 m2. In all, 24 whole-plant taxa of various growth forms were identified. This assemblage represents a lepidodendrid- and Cordaites borassifolius-dominated forest, with a well-developed understory of subarborescent lycopsids, tree ferns, medullosan pteridosperms, and calamites, as well as herbaceous ground cover. Lycopsids were dominated by Lepidodendron simile bearing Flemingites-type cones and L. lycopodioides; Lepidophloios cf. acerosus was subdominant. Lianas, mostly lyginopterid pteridosperms and some ferns, were usually found close to upright stems. The ground cover, mostly ferns and sphenophyllaleans, was taxonomically the most diverse stratum, although only a minor contributor to the peat. Based on samples from the coal roof, the palynological record is in agreement with the tuff bed assemblage except for the quantity of certain taxa. To reduce this bias, compression R-values were calculated from the percent cover of aerial plant parts in the excavation and in the dispersed palynoflora. These R-values suggest that in the palynological record, arborescent lycopsids and sphenophylls are greatly overrepresented, ferns and cordaites strongly underrepresented, and calamites are almost the same in both records.

Stephanian Fossil Flora from Paralic Carboniferous Deposits of the Jesenice Area (Slovenia) and Its Comparison with Czech Localities

Abstract This paper provides documentation of the Late Carboniferous flora of the Southern Karavanke Mountains in Slovenia that is housed in the Gornjesavski Muzej (Upper Sava Museum) in Jesenice, Slovenia. The paleoflora from this area has not been systematically documented until today. 21 fossil-species, which probably represent 17 biological species, were identified. Common species include Sigillaria brardii Brongniart, Lepidodendron dissitum Sauver, Annularia carinata Gutbier, Calamites undulatus Sternberg, Sphenophyllum oblongifolium (Germar and Kaulfuss) Unger, Acitheca polymorpha (Brongniart) Schimper and Nemejcopteris feminaeformis (Schlotheim) Barthel. Stratigraphically important are Sphenophyllum oblongifolium and Nemejcopteris feminaeformis, and based on their occurrence we can assume the studied paleoflora to be Gzhelian D (Jigulites jigulensis zone on the Russian Platform), i.e. Stephanian C

REVISION OF THE PENNSYLVANIAN FLORA FROM VAL SANAGRA IN WESTERN PART OF THE SOUTHERN ALPS (ITALY)

Abstract The Pennsylvanian flora from the Alpe Logone/Val Sanagra locality in the Western Lombardy (Southern Alps, Italy) last underwent a taxonomic study in the mid 20th century. The main problem is generally poor preservation of the plant remains, which makes their identification problematic. Despite this, the authors have identified 43 fossil species from this locality. Based on the sedimentary context of this paleoflora, we assume that the Val Sanagra sediments were deposited in a continental setting, in a fluvial environment with a well-developed and vegetated floodplain where where clastic substrates would locally and occasionally change into peat swamp. The common presence of rhytidolepis and sub-rhytidolepis sigillarias, as well of Eusphenopteris neuropteroides, Lobatopteris miltonii, Mariopteris latifolia, Paripteris linguaefolia, Pecopteris microphylla, Alethopteris sp. (cf. grandinii) indicates that the flora from the Val Sanagra locality spans the interval between the Duckmantian and Bolsovian (middle Moscovian), and thus represents one of the oldest Pennsylvanian floras of the Southern Alps.

Significant hiatuses in the terrestrial Late Variscan Central and Western Bohemian basins (Late Pennsylvanian–Early Cisuralian) and their possible tectonic and climatic links

Abstract Significant changes in the stratigraphy of the Central and Western Bohemian Upper Palaeozoic basins occur during or shortly after hiatuses. The different extent and changes in the depocentres of the Radnice and Nýřany members (Moscovian) in the Plzeň Basin clearly indicate changes in the structure of this basin taking place during a break in sedimentation between these two units (311.9–308.3 Ma). Thick weathered rocks that occur in boreholes in the Mšeno–Roudnice Basin indicate another sedimentation break (305.9–304.1 Ma) between the Nýřany Member and the Týnec Formation (Kasimovian). Another possible hitherto undiscovered hiatus occurred between the Týnec and Slaný formations (Kasimovian–Gzhelian, about 304–303 Ma). The most significant changes in the configuration of the basins occurred between the Slaný and Líně formations (Gzhelian–Asselian, 301.6–300.6 Ma). This is indicated by deeply cut river valleys at the top of the Slaný Formation, by high thickness of weathered deposits occurring immediately beneath the Líně Formation, and mainly by the shift of depocentres from the southern to the northern part of the Central Bohemian basins. The hiatuses between the Radnice and Nýřany members and between the Slaný and Líně formations are accompanied by significant changes in the depocentres, and they are therefore interpreted primarily as tectonic events related to the extensional collapse of the Variscan orogenic belt. By contrast, the hiatuses beneath and above the Týnec Formation are interpreted as being the products of lower sedimentation rates during drier climates, which is consistent with the characteristics of the sediments, correlation with other Central European basins, and with climate models for this period. Due to the characteristics of the Líně Formation, in which the effects of climate aridization are clearly seen, the authors presume that tectonic as well as climatic changes occurred at the hiatus between the Slaný and Líně formations.

Comparison of structures derived from mine workings and those interpreted in seismic profiles: an example from the Kačice deposit, Kladno Mine, Bohemia

Abstract Five seismic profiles across the Kačice coal deposit were reinterpreted and compared with observations in mine galleries. The comparison shows that approximately 80% of normal faults with displacement exceeding 5 m detected on the seismic profiles really exist. In contrast, in only two cases have mine workings shown faults (vertical displacement 10–15 m) that have not been identified by seismic measurements. Discrepancies may be mostly explained by: (i) misinterpretation of the fault with slope of the presedimentary palaeorelief accompanied by differential compaction; (ii) virgation of faults and misinterpretation of a fault zone composed of several small faults individually below the detection limit but whose aggregate displacement is detected, giving the appearance of a single fault; (iii) faults which die away toward the overburden indicating synsedimentary movements in the deposit.